Use MicroBuildSigningPlugin from arcade templates and split .vsts-dotnet.yml

[YuliiaKovalova]

Use MicroBuildSigningPlugin from arcade templates
internal run: https://dev.azure.com/devdiv/DevDiv/_build/results?buildId=11968230&view=results

• split .vsts-dotnet.yml to prod and test pipelines

[Copilot]

Pull Request Overview

This PR switches to using the MicroBuildSigningPlugin via the shared arcade job template and removes the explicit signing and cleanup tasks.

• Adds a job.yml template invocation with enableMicrobuild: true
• Removes the manual MicroBuildSigningPlugin task
• Removes the manual MicroBuildCleanup task

Comments suppressed due to low confidence (2)

.vsts-dotnet.yml:95

• Ensure that the enableMicrobuild: true parameter in the template covers the signing conditions (e.g., SignType checks) previously handled by the explicit task; otherwise, artifacts may be signed when not intended.

      - template: /eng/common/templates-official/job/job.yml@self

[JanProvaznik]

the internal job doesn't run and requires some approval, I saw something similar in FR, I guess just ask them to allow it?